Note: Descriptions are shown in the official language in which they were submitted.
WO 92/20915 ~~ ~ ~ ~ PCT/AU92/00216
1
Fuel system for a fuel infected enoine
This invention relates to a fuel system for delivering metered
quantities of fuel to an internal combustion engine and is particularly
applicable to
fuel systems incorporating a fuel injector which can deliver fuel either
directly to the
engine combustion chamber or to the air induction system of the engine.
It is customary to provide in a fuel injection system a fuel pressure
regulator to maintain the fuel supply at a preset pressure, as the pressure of
the fuel
is relevant to the process of metering the fuel to the engine. Where a
conventional
1 0 pressure regulator is used, it is necessary to provide a fuel return line
from the
regulator to the fuel reservoir, thus effectively doubling the length of fuel
line
between the fuel reservoir and the fuel injection equipment that convey fuel
at high
pressure. The increase in fuel line length represents an expense in both the
supply of
material and assembly thereof, and also significantly increases the risk of
high
1 5 pressure fuel leakage developing.
From the point of view of safety, and also economy, it is desirable to
reduce the extent of fuel lines between the fuel reservoir and the engine.
This is
particularly so in marine engine installations where leaked fuel can collect
in an
enclosed area and present a major fire hazard.
2 0 More importantly the energy consumed in pumping fuel at a rate
substantially in excess of the engine fuel requirement represents a
significant energy
waste. Currently the fuel pump in a fuel injection system is normally
electrically
driven and operates continuously, thus consumes substantial electrical energy
circulating fuel that is not required. This energy waste particularly occurs
during
2 5 low to medium load and/or speed operation of the engine and as the energy
to drive the
fuel pump is supplied directly or indirectly from the engine, energy wasted in
pumping excess fuel represents a significant component of the fuel consumption
of the
engine.
There has been proposed such as in U.S. Patent No.'s 3,967,598 and
4,565,173, fuel injection systems wherein the fuel pump is operated cyclically
so as
to maintain a substantially constant fuel supply pressure to the injector, and
also so
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as to avoid the necessity of providing a return fuel circuit from the pump to
the fuel tank
or reservoir.
In both of these proposals, the fuel pump is required to operate at a duly
cycle, directly related to the injection frequency, which in turn is related
to engine
speed. A pump operating on a duty cycle of such high frequency inherently has
a low
pumping efficiency, and consequently a low energy consumption efficiency.
Further, the
operation of a pump in a high frequency cycling mode severely reduces the life
of the
pump.
Although the fuel system proposed in US patent 3,967,598 does provide
an accumulator downstream of the fuel pump, the pump is still required to
operate on a
cyclic basis at a frequency equal to the frequency of injection. The
accumulator is only
provided for the purpose of attempting to substantially maintain the designed
pressure
for the supply of fuel to the injector and to overcome mechanical and
hydraulic induced
time delays which would otherwise prevent the attaining of substantial
synchronism
between the injector cycle and the pump cycle.
It is the object of the present invention to provide a method and apparatus
for the supply of fuel to an engine which enables the maintenance of accurate
metering of
the fuel to the engine in accordance with the engine fuel demand avoids the
necessity of a
high pressure fuel return line to the fuel reservoir and improve the
operational
efficiency of the fuel pump.
With this object in view there is provided according to the present
invention a method of operating a fuel system supplying metered quantities of
fuel for
delivery to an internal combustion engine, said system having a cyclically
operable fuel
pump, a metering means to receive fuel supplied by the pump, and a processor
to control
the metering means to deliver a metered quantity of fuel to the engine, said
processor
determining the metered quantity of fuel required by the engine in response to
signal
inputs thereto indicating engine operating conditions, said method including
intermittently operating said pump under control by the processor to maintain
a fuel
supply to the metering means at a pressure between selected limits, said
limits being
selected so that the pump means delivers during each period of operation a
quantity of
fuel greater than a multiple of the maximum single metered quantity of fuel
deliverable
by the metering means, and sensing the pressure of the fuel supply to the
metering
means, and inputting to the processor a signal indicative of the sensed
pressure, said
processor applying said fuel pressure signal in the control of the metering
means to
deliver the required quantity of fuel.
IPEA/SUBSTITUTE SHEET
WO 92/20915 ~ ~ R ~ ~ ~ PCT/AU92/00216
3
Conveniently the fuel is supplied by the pump to a chamber,
preferably a closed chamber, from which the fuel is directly supplied to the
fuel
metering means. The chamber may act in the manner of an accumulator, and a
pressure sensor provides the input signal to the processor indicative of the
pressure
of the fuel available to fuel metering means from the accumulator.
The processor can be adapted to control the operation of the fuel pump
in accordance with the pressure input signal so that the pressure of the fuel
in the
accumulator is maintained between the selected maximum and minimum pressures.
Alternatively, the cycling of the pump may be controlled by an input signal to
the
1 0 processor indicative of the fuel level in the chamber or by a fuel level
sensor directly
controlling the operation of the pump.
It will be appreciated that the pressure of the fuel supplied to the fuel
metering means will influence the rate of delivery of the fuel by the metering
means
such as the rate of flow of the fuel through a metering orifice. Thus the
processor is
1 5 required to take account of the pressure of the fuel supply in the control
of the
quantity of fuel delivered to the engine. Normally the fuel metering means
includes a
selectively opening port or nozzle and the period of opening of the nozzle or
port is
varied to control the amount of fuel delivered. Thus a variation in the
pressure drop
across the nozzle or port will influence the rate of fuel flow when the port
or nozzle is
2 0 opened, and the processor can control that period in accordance with the
pressure of
the fuel supplied to the port or nozzle together with other engine operating
conditions
to achieve delivery of the correct amount of fuel. The fuel pressure sensor
may
alternatively be arranged to sense the pressure differential between the fuel
supply
and a gas into which the fuel is delivered during metering. This input can
similarly be
2 5 used by the processor in achieving accurate metering of the fuel.
The above fuel supply system has the advantage that no pressurised
fuel return line is required from the high pressure side of the pump, and the
pump is
only operated to meet the actual fuel demand of the engine, thus representing
a
substantial saving in energy which would normally be used merely to pump fuel
from
3 0 the reservoir which was subsequently returned to the reservoir. Further as
the
processor receivers an input indication the actual pressure of the fuel supply
to the
fuel metering means it is not necessary to maintain the fuel supply pressure
substantially constant. Accordingly the fuel pump can be operated on a no-
regular
intermittent basis with substantial time intervals between successive
operating
3 5 period. The pump can thus operate at the designed speed at high efficiency
and low
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overall energy consumption and reduced wear rate.
In addition, by having a sensor to deliver a signal to the processor to
indicate the actual pressure of fuel available to the fuel metering means, no
pressure
regulation is required and the processor alone can accurately control the fuel
metering
means to ensure the correct fuel quantity is delivered to the engine to meet
the fuel
demand thereof at all fuel supply pressures.
Currently there are in use fuel injection systems wherein the metered
quantity of fuel is delivered to the engine entrained in a gas, usually air.
In such
injection systems it is common to effect the metering of the fuel as it is
delivered into the
gas and thus the pressure of the gas is relevant to the fuel metering process.
Accordingly, when the fuel supply pump is intermittently operated, to control
the
pressure of the fuel supply to the fuel metering means, the processor may be
arranged to
be varied the pressure of the fuel supply in response to variations in the
pressure of the
gas into which the fuel is metered to control the pressure differential
therebetween.
Thus a substantially constant pressure differential can be maintained between
the fuel
and gas. Alternatively the pressure differential between the fuel and the gas
can be
sensed and controlled to achieve the substantially constant pressure
differential.
Also it is desirable under some engine operating conditions to vary the
pressure of injection of the fuel or fuel - gas mixture to the engine. This
can be achieved
with the presently proposed fuel supply system due to the ability to vary the
fuel supply
pressure without adversely affecting the fuel metering process.
There is also provided according to the present invention a fuel system for
an internal combustion engine, said system comprising a fuel pump for
delivering fuel
from a fuel reservoir to a fuel metering means, including an intermediate
reservoir
downstream of the fuel pump, sensor means to generate a signal indicative of
the
pressure of the fuel in the intermediate reservoir, and a processor to receive
and process
said signal to maintain said pressure of the fuel in the intermediate
reservoir within
predetermined limits by selectively switching the fuel pump on and off.
Preferably the
processor also responds to the pressure of the fuel supply in the intermediate
reservoir
in the control of the fuel metering means to meet said fuel demand, whereby
the accuracy
of the fuel metering is not adversely affected by the cycling of the operation
of the pump.
IPEAISUBSTITUTE SHEET
WO 92/20915 ~ O ~ 5 ~ ~ PCT/AU92/00216
The invention will be more readily understood from the following
description of one practical arrangement of the fuel system as illustrated in
the
accompanying drawing.
Figure 1 is a schematic representation of the fuel system particularly
5 applicable to marine engines.
Referring now to Figure 1, the plurality of fuel metering and injector
devices 10 are arranged so that each device delivers fuel to a respective
cylinder or
cylinder inlet port of a multi-cylinder engine. It is to be understood that
the number
of fuel metering and injector devices will vary with the character of the fuel
system
1 0 and there may be a single device even for a multi-cylinder engine.
Each of the fuel metering and injector devices 10 receive fuel from a
common fuel rail 11 which is supplied with fuel from the fuel reservoir 12. As
the
installation shown is for use in marine applications, the fuel reservoir 12 in
turn
receives fuel from the remote fuel tank 13 via the lift pump 14. The fuel
reservoir
1 5 12 is fitted with a float valve 9 which will close to prevent the delivery
of fuel by the
lift pump 14 when the fuel level in the reservoir 12 has reached a preset
level. The
provision of the fuel reservoir 12, lift pump 14 and float valve 9 are for the
purposes of complying with U.S. regulations relating to marine engines. These
regulations do not apply in other installations such as automobiles or other
motor
2 0 vehicles, in which installations the fuel reservoir 12 would be the
conventional fuel
tank of the vehicle.
The high pressure fuel pump 15 draws fuel from the reservoir 12 and
delivers it to the accumulator 16 via the fuel filter 17. The accumulator 16
is in the
form of a closed chamber having at least one deflectable or movable wall 19
which is
2 5 preloaded by the spring 20 or the like resilient component. The wall 19 is
displaced
or deflected upwardly as viewed in Figure 1 by the pressure of the fuel and as
fuel is
delivered to the accumulator and downward by the spring as fuel is withdrawn.
Thus
the pressure of the fuel in the accumulator can be maintained within preset
limits
while fuel is being delivered therefrom to the fuel rail 11 and hence to the
metering
3 0 and injector units 10. The accumulator 16 may alternatively be constructed
to
maintain a near steady pressure of the fuel therein with the fuel level moving
between
set upper and lower levels with a position sensor to issue a signal to
indicate the fuel
level.
The pressure sensor 18 is responsive to the pressure of the fuel in the
3 5 accumulator 16 or anywhere upstream thereof and down stream of the
injector
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WO 92/20915 PCT/AU92/00216
6
devices 10, and generates a signal for input to the ECU 22 which is programmed
to
switch the pump 15 on and off so as to maintain the pressure in the
accumulator 16
between preset maximum and minimum values. Thus when the rate of fuel
consumption is low the pump will be switched off for long periods until
sufficient fuel
is consumed from the accumulator to allow the pressure to drop from the
maximum to
the minimum preset value. Even at maximum fuel consumption rates, the
operation of
the fuel pump 15 will be cycled on and off as the capacity of the accumulator
is
selected to be a multiple of the maximum fuel consumption rate per cycle of
the
injector system. It will be apprecaited that a similar cycling of the pump
operation
1 0 will be obtained by the ECU 22 receiving signals from position sensors
indicating the
fuel level in the accumulator. The capacity of the accumulator and the
permitted
variation in fuel pressure or fuel level therein is preferably selected is
that, even at
maximum fuel consumption rate, the pump is switched on at intervals
corresponding
to 50 or more fuel deliveries by the injectors. The on and off cycling of the
fuel pump
1 5 will provide a substantial reduction in energy consumption by the fuel
system,
particularly consumption of energy in the form of electrical power generated
by an
alternator driven by the engine. This saving is particularly significant when
the
engine is operating at low to medium loads and/or speeds.
The signal input to the ECU 22 by the pressure sensor 18 is also used
2 0 in the control of the fuel metering component 23 of the fuel metering and
injector
devices 10 so that in determining the amount of fuel required each fuel
delivery event,
account will be taken of the actual fuel pressure at that point in time. This
enables the
accurate calculation of the required period of opening of the fuel metering
component
to deliver the quantity of fuel calculated to meet the fuel demand of the
engine.
2 5 The ECU also receives the conventional inputs for determination of the
engine fuel demand such as engine speed, engine load and engine temperature.
As the fuel pump 15 only operates when fuel is required to maintain
the fuel supply within the preset pressure or level limits, it is not
necessary to
provide a return line from the fuel rail 11 to the reservoir 12. However, for
other
3 0 reasons, such as to ensure against the accumulation of fuel vapour in the
fuel rail 11,
having regard to the temperature of the environment in which the fuel rail is
located,
it can be desirable in some installations to provide for the bleeding of a
small amount
of fuel back from the fuel rail to the reservoir 12. This can be achieved by
providing
an appropriate return line 21 which incorporates a flow control orifice 24
selected so
3 5 that the amount of fuel returned to the reservoir 12 is only that
sufficient to prevent
CA 02108667 2000-12-20
7
vapour accumulating in the rail ti. A solenoid actuated valve may be provided
in the
return line 21 which is opened under the control of the ECU 22 in accordance
with a
preset cycle or in response to operating conditions such as engine
temperature,
start-up conditions or fuel temperature.
The above described method and apparatus for supplying fuel to an
engine is applicable to fuel injection systems wherein fuel alone or fuel and
gas such
as air are delivered to the engine, including fuel injector systems wherein
the
metered quantity of fuel is entrained in air prior to or during injection. A
typical
construction of such a fuel metering and injeciton system is disclosed in US
Patent No.
1 0 4,934,329 ,
In a fuel injection system wherein the fuel is metered into air to be
carried thereby to the engine, the ECU. 22 can also receive an input signal
indicative of
the pressure of that air to be used in controlling the fuel metering. Also air
at that
pressure, which may to sub-atmospheric, can be applied to the movable wall -19
of
~ 5 the accumulator 16 to complement the load applied by the spring 20. In
this
arrangement the pressure of the fuel in the accumulator will be related to the
air
pressure in a preset manner. This is beneficial in the fuel metering operation
in that
a substantially steady pressure differential can be achieved between the fuel
and air
supplies. It can also be desirable to increase the gas pressure at high load
operation of
2 0 the engine relative to the pressure at low to medium load conditions, or
in relation to
engine speed either alone or in combination with engine load. The processor
can be
arranged to determine when such a gas pressure charge is to be effected by
input
signals indicating engine load and/or speed or in response to the fuel
requirement of
the engine being above a predetermined level.
